Thin film resistance attenuator

ABSTRACT

A thin film resistance attenuator comprises more than two bandshaped insulation regions or band-shaped conduction regions selectively provided therein. The lengths of these regions are adjusted whereby the characteristic impedance and attenuation value of the attenuator are independently adjusted.

United States Patent Inventor Nobuyoshi Yoshida Tokyo, Japan Appi No 873,605 Filed Nov. 3. 1969 Patented Aug. 10, 1971 Assignee Nippon Electric Company, Limited Tokyo, Japan Priority Nov. 4, 1968 Japan 43/80842 THIN FILM RESISTANCE ATTENUATOR 5 Claims, 4 Drawing Figs.

us. Cl 333/81 R, 338/309 in. CI 1101p 1/22, H01 p 7/00 Field oiSearch 333/81,81

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Pau1 L. Gensier Attorney-Sandoe, Hopgood 8L Calimafde ABSTRACT: A thin film resistance attenuator comprises more than two band-shaped insulation regions or band-shaped conduction regions selectively provided therein. The lengths of these regions are adjusted whereby the characteristic impedance and attenuation value of the attenuator are independently adjusted.

I PATENTEDAusmlsn SHEU 1 [IF 2 FIG.I

(Prior Art) 03 qvvavroa Nobuyoshu Yoshido (Prior AH) FIG. 2 y

'II'IIN FILM RESISTANCE ATTENUATOR This invention relates generally to thin film resistance attenuators and, more specifically, to a thin film resistance attenuator adapted for adjustment of both its attenuation and characteristic impedance to specific values.

The known or prior art resistance attenuator consists of three resistance elements connected in the formof either a T or 1r, or of four resistance elements connected in the form of a bridge. Since resistance film is now easily fabricated by virtue of recent developments in thin film technology; a resistance film attenuator having excellent high frequency characteristics in comparison with the conventional resistance attenuators will in all likelihood be widely used in the near future.

However, in the production of a thin film type resistance attenuator based on thin film technology, it is impossible to make its dimensions perfectly coincident with the design values by depending solely on an etching process or the like. According to the prior art techniques; the resistance value of the attenuator must be precisely adjusted by a suitable process in the last stage of manufacture so as to establish the desired characteristic impedance and attenuation value. Practically, however, it is very difficult to adjust the resistance of the attenuator so as to simultaneously satisfy the characteristic impedance and attenuation value.

It is an object of the present invention to provide a thin film resistance attenuator capable of having its characteristic impedance and attenuation value independently adjusted.

The resistance attenuator of this invention has more than two band-shaped insulation regions or band-shaped conduction regions selectively provided therein. The lengths of these insulation regions or conduction regions are adjusted whereby the characteristic impedance and attenuation value of the attenuator are independently adjusted.

The above-mentioned and other features and objects'of the present invention and the manner of attaining them will become more apparent and the invention itself will best be understood by reference to the followingdescription of embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIGS. 1(a) through 1(d) are diagrams illustrating a'conventional thin film-resistance attenuator;

FIG. 2 is an equivalent circuit diagram of the resistance attenuator shown in FIG. 1(a);

FIG. 3 is a circuitdiagram redrawn from the circuit of FIG. 2 with the center line viewed as a reference; and

FIGS. 4(a) through 4(d) are diagrams illustrating various designs of thin filmtype resistance attenuators embodying features of the present invention.

FIGS. 1(a) through 1(d) illustrate examples of thin film resistance attenuators according to the prior art. FIG. 1(a) shows a resistance attenuator consisting of a pair of input terminals 13, a pair of output terminals 2-3, and a resistance film 4.

In FIG. 1(a), the three portions indicated by hatching denote electrodes connected to terminals 1 to 3. respectively. FIGS. 1(a) and 1(d) are diagrams of resistance attenuators in which the resistance film are respectively triangular and rhombic in shape. The terminals and electrodes of these resistance attenuators of FIGS. 1(0) and 1(a) are arranged in the same manner as in the resistance attenuator of FIG. 1(a).

FIG. 1(b) shows a resistance attenuator of the balanced circuit network type, having a pair of input terminals I-1' and a pair of output terminals 2-2. Four portions indicated by hatching represent the electrodes connected to these terminals.

The prior art attenuators of the type shown in FIGS. 1(a) through 1(d) are described in several published reports such as Synthesis of Multiple Resistance Networks from Single Resistive Films by R. 1. Dow, IEEE Transaction; Component Parts Vol. CP-lO of Dec. 1963, pp. l47-l55; Functional Tantalum Thin-Film Resistive Networks and Decoders by W. Worobey and R. W. Wyndrum, Jr., IEEE Transaction, Parts, Materials and Packaging Vol, PMP-4 of Mar. 1968, pp. 22- 29; and Triangular, Rhombic, and Distributed Resistance Networks and their Applications by S. C. Lee, IEEE Transaction, Parts, Materials and Packaging Vol. PMP-4 of June 1968, pp. 4l-50.

The film resistance attenuator shown in FIG. 1(a) is a socalled symmetrical-type resistance attenuator in which the characteristic impedance on the input side is equal to that on the output side. This resistance attenuator can be expressed generally by the equivalent circuit of FIG. 2, wherein it is known that the resistance values of the resistors 10, 1 l, 12 and 13 are uniquely determined when the values of the characteristic impedance and attenuation are given. The terminal numbers in FIG. 2 correspond to the numbers in FIG. 1(a). In the attenuator shown in FIG. 1(a), the current distribution in the operating condition is symmetrical with respect to the centerline CL of the figure. This centerline CL is a straight line being equally distant from the electrode of terminal 1 and from the electrode of terminal 2, and perpendicular to the electrode of terminal 3.

In the attenuator of FIG. 1(a), when terminals 1 and 2 are externally short circuited and a voltage is applied between these short-circuited terminals and terminal 3, the current distribution on the resistance film 4 is symmetrical with respect to the centerline CL. Therefore, if the resistance film in the portion of centerline CL is removed or a conductor is placed in this portion instead of the resistance film, the resistance value between terminal 3 and the terminal formed by short circuiting terminals 1 and 2 is unchanged. To better illustrate this point, the circuit of FIG. 2 may be redrawn as shown in FIG. 3 wherein the resistance value between terminal 3 and the terminal formed by short circuiting the terminals 1 and 2 is constant and equal to R +R /2 even when an arbitrary impedance is connected between terminals 23 and 24 (where R is the resistance value of resistor 13 and R is the resistance value of resistors 10 and 11), because the bridge circuit consisting of four resistance elements 10, ll, 16 and I7 is balanced. v

On the other hand, in the resistance attenuator of FIG. 1(a), the resistive value between terminals 1 and 2 depends on the conductivity of the resistance film of the portion of centerline CL. In other words, the value of resistance between terminals 1 and 2 is changed if the resistance film of the portion of centerline CL, or a conductive film is placed in the portion in place of the resistance film.

This function will be more specifically explained by referring to FIG. 3 in relation to FIG. 2. The resistance value between terminals 1 and 2 is influenced by the resistances between the terminals 21 and 22 and between the terminals 23 and 24. However, the value of resistance between terminals 1 and 2 is 2R,R /(2R +R,) and is not dependent upon R, (where R is the resistance value of resistor 12). On the other hand, it is well known that the characteristic impedance and attenua tion value of the attenuator shown in FIG. 2 are given by R. and 20 log, l+R,/R,,), respectively, and that the relationship between R,, R and R are given by R,XR,=R Therefore, when the desired characteristic impedance R and attenuation value are given as design values, the values R and R, are obtained from the above-mentioned relationship by calculation. Then, the desired values of R +R /2 and 2R,R /(2R +R,) are obtained by calculation.

FIG. 4(a) shows one embodiment of a thin film resistance attenuator of the present invention. This resistance attenuator is of the unbalanced type, having terminals 1, 2 and 3, thereby to form a pair of input terminals 1-3 and a pair of output terminals 2-3. Three band-shaped insulation regions 5, 6 and 7 are formed in a part of the resistance film 4 having a substantially uniform resistance per unit area. This resistance attenuator is the same as the conventional resistance film attenuator, except for these three insulation regions.

In the fabrication of the attenuator of FIG. 4(a), the bandshaped insulation region is not initially provided but rather is formed in the adjusting process which occurs during the last stage of manufacture. By forming this insulation region, it is possible to independently trim the attenuation and characteristic impedance of the resistance attenuator to their desired values.

Specifically, the resistance value between terminal 3 and the terminal formed by short circuiting terminals 1 and 2 is measured in the condition wherein the band-shaped insulation region is not as yet provided. As will be obvious from FIG. 2, this resistance value must be R +R 2. Generally, however, the resistance attenuator is manufactured with a smaller value of resistance than R +R /2. To make the resistance value equal to R +R /2, band-shaped insulation regions and 6 are formed to increase the resistance to the desired value. This process is carried out while measuring the resistance value between terminal 3 and the terminal formed by short circuiting terminals 1 and 2. Practically, the band-shaped insulation regions 5 and 6 are started from the edge of the resistance film 4; the band-shaped insulation region 5 is then extended gradually toward the right, and insulation region 6 toward the left. These insulation regions may be formed, for example, by mechanically destroying the thin film resistance body.

Because the resistance attenuator of FIG. 4(a) is of the symmetrical type, the band-shaped insulation regions 5 and 6 are formed so that the resistance value between terminals 1 and 3 is equal to the value of resistance between terminals 2 and 3. For forming these insulation regions, therefore, it is necessary to employ means for either intermittently or continually monitoring these values.

The resistance value between terminals 1 and 2 is then measured. As is obvious from FIG. 2, this resistance value must be 2R R /(2R +R,). In general, however, the resistance value is smaller than 2R,R 2R +R,) during the manufacturing process even after forming the band-shaped insulation regions 5 and 6. To make the resistance value equal to 2R,R /(2R +R the band-shaped insulation region 7 is formed, thereby to increase the resistance value between terminals 1 and 2 to the desired value. This process is done while measuring the resistance value between terminals 1 and2. The insulation region 7 is started from the edge of the thin film resistance body, and is extended gradually toward the lower direction. As described, since the resistance value between terminal 3 and the terminal formed by short circuiting terminals 1 and 2 is not influenced by the band-shaped insulation region 7, the resistance value between terminal 3 and the terminal formed by short circuiting terminals 1 and 2 for which the adjustment has been completed is kept constant even when the insulation region 7 is formed. From this point of view, the thin film type resistance attenuator having the insulation regions 5, 6 and 7 is a resistance attenuator which simultaneously satisfies the desired values of characteristic impedance and attenuation.

The thin film type resistance attenuator of FIG. 1(a) has already been described above. Similarly, in the attenuators shown in FIGS. 1(b), 1(a) and 1(d), the resistance value can be trimmed to simultaneously satisfy the characteristic impedance and the amount of attenuation by forming similar band-shaped insulation regions.

FIGS. 4(b), 4(0) and 4(d) show examples of film resistance attenuators having band-shaped insulation regions similar to those shown in FIG. 4(a) as incorporated in the resistance attenuators of FIGS. 1(b), 1(0) and 1(d), respectively. Particularly, in the balanced circuit network attenuator shown in FIG. 4(b), the resistance value between terminals 1 and 2 or terminals l and 2' and the other resistance value between a terminal formed by short circuiting terminals 1 and 2 and another terminal formed by short circuiting terminals I and 2' can be independently adjusted.

The band-shaped insulation regions 5 and 6 shown in FIG. 4(a) are formed in the boundary between electrode 3 and the thin film resistance body. Needless to say, these insulation regions may not be located in the boundary; for example, the

band-shaped insulation region 5 may be disposed between the electrode connected to terminal 1 and the resistance film; and the band-shaped insulation region 6 may be disposed between the electrode of terminal 2 and resistance film 4. Furthermore, these insulation regions may be located not only between the electrode and the boundary, but also on the thin film resistance body. The band-shaped insulation region 7 must be on the centerline CL and may not be started from the edge of the thin film resistance body. The thin film type resistance attenuators of FIGS. 4(b), 4(a) and 4(d) may be modified in the same manner as above.

A method has been described in which a band-shaped .insulation region is formed on the resistance film of a thin film resistance attenuator and the resistance value is increased and then trimmed. As a modification, a band-shaped condition region may be formed by applying conductive paste at the position of the band-shaped insulation region, thereby to lower the resistance value for purposes of trimming.

While only several embodiments of the present invention have been herein specifically disclosed, it will be apparent that variations may be made therein without departure from the spirit and scope of the invention.

I claim:

1. A thin film resistance attenuator comprising a thin film of resistive material substantially fiat in shape and divided into first and second areas symmetrical with respect to a reference line,

a first thin film area of conductive material in contact with said first resistive material film area at its marginal portion excluding said reference line,

a second thin film area of conductive material in contact with said second resistive material film area at its marginal portion excluding said reference line, said second conductive material film area being positioned substantially in symmetry with said first conductive material film area with respect to said reference line;

a third thin film area of conductive material in contact with said resistive material film at its marginal portion, said third conductive material film area being symmetrical with respect to said reference line;

first, second and third terminals attached to said first,

second and third conductive material film areas respectively,

a first strip on said resistive material thin film lying along said reference line, and second and third strips lying in said first and second resistive material film areas respectively, said first, second and third strips each having a resistivity different from the rest of said resistive material film and having lengths respectively adjusted to independently provide a desired resistance value between said first and second terminals and another resistance value between a terminal formed by short circuiting said first and second terminals and said third terminal, whereby a desired characteristic impedance and attenuation value of said resistance attenuator are obtained.

2. The attenuator of claim l, in which at least one of said strips is formed of insulative material.

3. The attenuator of claim 1, wherein at least one of said strips is formed of conductive material.

4. The attenuator of claim 1, in which said thin film is rectangular in shape, one of said strips extending vertically along said reference line from one horizontal edge thereof, and said pair of second strips extending horizontally from opposing vertical edges toward said reference line.

5. A thin film resistance attenuator comprising a thin film of resistive material substantially flat in shape nd divided into first and second areas symmetrical with respect to a reference line,

a first pair of conductive material film areas in contact with said first and second resistive material film areas respectively at those marginal portions excluding said reference line and positioned substantially in symmetry with respect to said reference line,

a second pair of conductive material film areas in contact with said first and second resistive material film areas respectively at those marginal portions excluding said reference line and said first pair of conductive material film areas and positioned substantially in symmetry with respect to said reference line,

first and second terminals attached to said first pair of conductive material film areas, respectively,

third and fourth terminals attached to said second pair of conductive material film areas, respectively; and

a first pair of strips on said resistive material film lying along said reference line and a second pair of strips lying in said first and second resistive material film areas, respectively,

said first and second pairs of strips each having a resistivity different from the rest of said resistive material film and having lengths respectively adjusted to independently provide a desired resistance value between said first and second terminals or said third and fourth terminals, and another resistance value between a terminal formed by short circuiting said first and second terminals and another terminal formed by short circuiting said third and fourth terminals, whereby desired characteristic impedance and attenuation value of said resistance attenuator area obtained. 

1. A thin film resistance attenuator comprising a thin film of resistive material substantially flat in shape and divided into first and second areas symmetrical with respect to a reference line, a first thin film area of conductive material in contact with said first resistive materiAl film area at its marginal portion excluding said reference line, a second thin film area of conductive material in contact with said second resistive material film area at its marginal portion excluding said reference line, said second conductive material film area being positioned substantially in symmetry with said first conductive material film area with respect to said reference line; a third thin film area of conductive material in contact with said resistive material film at its marginal portion, said third conductive material film area being symmetrical with respect to said reference line; first, second and third terminals attached to said first, second and third conductive material film areas respectively, a first strip on said resistive material thin film lying along said reference line, and second and third strips lying in said first and second resistive material film areas respectively, said first, second and third strips each having a resistivity different from the rest of said resistive material film and having lengths respectively adjusted to independently provide a desired resistance value between said first and second terminals and another resistance value between a terminal formed by short circuiting said first and second terminals and said third terminal, whereby a desired characteristic impedance and attenuation value of said resistance attenuator are obtained.
 2. The attenuator of claim 1, in which at least one of said strips is formed of insulative material.
 3. The attenuator of claim 1, wherein at least one of said strips is formed of conductive material.
 4. The attenuator of claim 1, in which said thin film is rectangular in shape, one of said strips extending vertically along said reference line from one horizontal edge thereof, and said pair of second strips extending horizontally from opposing vertical edges toward said reference line.
 5. A thin film resistance attenuator comprising a thin film of resistive material substantially flat in shape and divided into first and second areas symmetrical with respect to a reference line, a first pair of conductive material film areas in contact with said first and second resistive material film areas respectively at those marginal portions excluding said reference line and positioned substantially in symmetry with respect to said reference line, a second pair of conductive material film areas in contact with said first and second resistive material film areas respectively at those marginal portions excluding said reference line and said first pair of conductive material film areas and positioned substantially in symmetry with respect to said reference line, first and second terminals attached to said first pair of conductive material film areas, respectively, third and fourth terminals attached to said second pair of conductive material film areas, respectively; and a first pair of strips on said resistive material film lying along said reference line and a second pair of strips lying in said first and second resistive material film areas, respectively, said first and second pairs of strips each having a resistivity different from the rest of said resistive material film and having lengths respectively adjusted to independently provide a desired resistance value between said first and second terminals or said third and fourth terminals, and another resistance value between a terminal formed by short circuiting said first and second terminals and another terminal formed by short circuiting said third and fourth terminals, whereby desired characteristic impedance and attenuation value of said resistance attenuator area obtained. 